Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: keithp on December 07, 2014, 10:30:24 AM
-
I assembled my BeePre and completed the resistance check successfully. After inserting the tubes and turning on the power, all 8 diodes on the C4S boards glowed as expected. During the voltage test I must have touched something I shouldn't have touched because I saw a spark and heard a pop. The two diodes on the B side of the C4S board went out. I rechecked my resistance readings and everything was good except terminal 11 which showed 0 resistance instead of the expected 30 kOhms +. The voltage at terminal 11 was down to 128 V instead of the expected 146 V. Several other voltage readings were also out of spec. I believe I blew the PN22907A transistor because two of the leads were shorted. Do I need to replace the diodes when I replace the transistor? Does the blown transistor explain the low voltage?
-
Yes, replace the transistors. The diodes are likely OK, but it won't hurt to replace them as well. Can you post all your voltages that are out of spec?
-
Thanks for your help. The other voltages that were lower than spec were D7 and D9, both were 122 V vs. the specified 147. Terminal 17 was higher than specified at 117 (90 to 110 specified).
-
Is POS out about where it should be?
-
I am having a really bad day. POS is 9.7. I remeasured some of the terminals. D9 had increased to over 180(?) While probing D7 I accidentally hit the ground lug and now the other two diodes on the left C4S are also out. When I get the replacement parts, I will check the rest of the C4S board for collateral damage. I guess I should be prepared to replace all four diodes and two transistors. Is there anything else I need to check before ordering the replacement parts?
-
Yes, that's a good plan. One thing you can do to make probing easier is to wrap all the metal except the tip of the probe in tape.
-PB
-
That's a good idea. Thanks for the tip.
-
Keith,
Heat shrink works well on the probes too.
Jim